Means for preventing pulsating in heating devices



Aug. 19, 1941. 1.. E. ARNOLD 2,253,414

MEANS FOR PREVENTING PULSATING IN HEATING DEVICES "3 Sheets-Sheet 1 loads .1? Qrnold Au 19, 1941. I l L, E, AR OLD 2,253,414

MEANS FOR PREVENTING PULSATING IN HEATING DEVICES Filed Oct. 6, 1937 I 5 Sheets-Sheet 2 Jami? Urnald v MJM gum g- 4 E. ARNOLD I I 2,253,414

MEANS FOR PREV NTING PULSATING IN HEATING DEVICES Filed Oct. 6, 1937 3 Sheets-Sheet 3 @QWJOW Jami. Ornald Patented Aug. 19; 1941 MEANS FOR PREVENTING PULSATING 1N nns'rmo nnvrcss Louis it. Arnold, Moiine, 111., assignor to The George Evans Co p ration. Moline, 111., a corporation of Illinois Application October 6, 1937, Serial No. 167,499

Claims.

This invention relates to an apparatus for preventing pulsating in heating devices. It-is particularly applicable to domestic oil burning furnaces, and it will be described in connection with such a furnace, although it is to be understood that it may also be used with other heating devices.

When oil burners are used with furnaces having combustion chambers that are substantially pressure tight except for the draft exit, there is a'limit to the magnitude of combustion that may occur in the furnace without encountering the phenomenon known as panting, or pulsating, of the combustion flame. This "panting is not only undesirable because of the noise and the vibrations that it causes, but also because it causes inefficient combustion and requires a larger furnace for a given capacity, than might otherwise be necessary. The present invention is directed to overcoming this difficulty under all conditions under which it tends to occur.

The general object of the invention is to provide an apparatus for preventing pulsating, or panting, in furnaces.

Other objects and advantages of the invention will appear from the following specification and drawings.

An embodiment of the invention is shown in the accompanying drawings in which:

Figure 1 is a side elevation of a furnace embodying an apparatus for practicing the invention;

Fig. 2 is a partial horizontal section of sai furnace on the line 2--2 of Fig. 1;

Fig. 3 is an enlarged side elevation of the oil burner shown in Fig. 1, a portion of the air tube being cut away;

. and sides, but open at the top. It is preferably Fig. 4 is a detail end elevation of the closure for the end of the air tube;

Fig. 5 is a detailed sectional elevation of the front end of the air tube;

Fig. 6 is a detailed sectional elevation of a burner showing a modified form of apparatus;

and

Fig. 'l is an end view of the air tube of Fig. 6

showing the air deflector in the end of said tube.

may be used with other types of substantially.

pear-shaped in cross section as shown in Fig. 2.

Above the fire box is a space II that receives the combustion gases which then pass rearwardly through the passages, or fiues I3, to a pipe 14 that leads to the stack or chimney. The fire box and the surrounding housing form an enclosed combustion chamber in which the oil is burned.

The air to be heated is drawn downwardly through the duct l5, through the cleaning screens i6, and around the pipe I, by a motor-driven blower ll. It is then forced upwardly through the spaces I (Fig. 2) between the ilue's l3 from where it passes upward through'the passage I9 to the various ducts leading about the building. The air is thus cleaned, pre-heated, heated, and then forced throughout the building.

An oil burner 20 of any of the many wellknown types on the market may be used. Such a burner has an electric motor 2| which forces all through the feed pipe 22 (Fig. 5) into the fire box in a fine spray, and which also drives a fan that forces air into the fire box through an air tube 23, which ordinarily has an air deflector in its end that causes the air to swirl as it enters the fire box, Such a deflector 24 is shown in Figs. 6 and 7. This deflector leaves the end of the tube quite open and in free communication with the fire box. Suitable electrical ignition points 25 (Fig. 3) are provided to ignite the mixture, and the burner is provided with automatic controls (not shown) to start and stop it in a manner well known in the art.

A finished ornamental casing 28 surrounds the heating chamber and burner to give the comdrives the oil pump and the air blower, and a quantity of atomized oil and air is forced into the combustion chamber where an electric spark ignites the mixture, When ignition takes place there is a sudden increase in thevolume of gases within the combustion chamber, and the only exit for these gases is through the furnace and chimney. This increased volume of gases and air have before them the column of air, or air and gases, extending from the combustion chamber to the top of the chimney. It would be necessary for this column to move instantly toward the top of the chimney in order to prevent the pressure within the combustion chamber from rising. This column, having weight and being subject to the laws of inertia and momentum, resists any sudden force tending to put it into motion, with the result that pressure within the combustion chamber increases.

The air supplied to the combustion chamber is supplied by a blower which is adjusted to deliver the proper quantity of air for emcientcombustion against the normal pressure within the combustion chamber. When the above-mentioned abnormal pressure occurs, the blower fails to supply enough air to complete the combustion and, under these circumstances, the combustion is incomplete. This results in a reduced volume of combustion gases as well as allowing some unburned fuel to accumulate. As a result of this ineflicient combustion, the pressure within the combustion chamber decreases. In the meantime, the column of gases leading from the chamber to the top of the. chimney has been given some motion through the high pressure condition that has just existed. This column resists any force tending to reduce its velocity. The movement of this column tends to reduce the pressure still more. The air blower is now confronted by an abnormally low resistance to the delivery of the air, with the result that the quantity of air delivered increases above normal. This increase in air, together with the unburned fuel which has accumulated during the low pressure period, combine and the result is that the combustion is greater than normal, which, in turn produces another high pressure condition. These high and low pressure periods follow each other in rapid succession and tend to resolve themselves into a rhythmic cycle known as panting."

The above-explained condition takes place at the starting of the furnace, and is sometimes designated the starting surge." It may continue for only a short period or it may continue indefinitely, dependingupon conditions.

Panting may also occur while the furnace is running, either as a continuation of the starting surge or as an independent phenomenon caused by variations in the combustion which start up the rhythmic. cycle above mentioned.

When the burner is shut off by opening the switch, the motor slows down. .At the instant the burner is shut off, the air blower is delivering the proper quantity of air to the combustion chamber but, as soon as the motor starts to slow down, the delivery diminishes very rapidly. At the same time, the column of air and gases from the combustion chamber to the chimney is moving outward at a certain velocity. As the speed of the motor decreases the air delivered to the blower diminishes rapidly while the air colunm from the chamber to the chimney 'top tends to continue to move. This produces a low pressure condiition within the combustion chamber which is followed by a high pressure period due to the tendency of the air to rush into the low'pressure combustion chamber. This phase of the phenomenon of panting" is very dimcult to investigate, owing to the fact that instruments sufliciently delicate and responsive are not available to obtain accurate proof of exactly what conditions exist. It is sumcient to say that the stoppin surge" or fflnishing kick is very similar to the starting surge" and consists of a series of rapid pulsations that make considerable noise and vibrate the furnace. V

Thus, the phenomenon of panting may occur when the furnace is started; it may occur during the period the furnace is running; it may take place when the furnace is stopped; and it may occur under any two or more of these conditions. The problem is to prevent it under all conditions.

It has been proposed to remedy the condition by'having an opening in the combustion chamber that will allow air to enter in case of a low pressure condition and allow gases to escape during a high pressure condition. This is undesirable owing to the fact that when the air enters the combustion chamber it is cold, it does not enter at the right place, it absorbs heat, and the thermal efllciency of the furnace is reduced. When a high pressure period occurs, the gases escape into the room where the furnace is, which is highly undesirable. While these gases might be vented to the outside of the furnace room, the resulting passage slows down the venting action and is not sensitive enough to give the desired results. This proposed arrangement is not satisfactory.

It has also been proposed to reduce the size of the combustion flame, but this reduces the efficiency of combustion, causes the deposit of soot, makes it impossible for the heating plant to deliver its greatest capacity, and is not a desirable solution.

I have found an inexpensive and eflicient method of handling this problem which prevents panting under all conditions. This method involves controlling the air supply in such a way that the "panting or pulsations, cannot get started. The method will be clearer by first describing it in connection with an apparatus for putting it into effect.

Referring to Figs. 1 and 3,-the blower 30 for forcing air into the air supply'tube 23 mm larger capacity than those normally employed for an 011 burner of a given capacity. The larger blower is used in order that a higher static pressure may be obtained, and continued under all working conditions, as will be presently explained.

This will be more clearly understood if the characteristics of a blower are briefly explained. A blower delivers its maximum volume of air in cubic feet per minute at zero or no static pressure. As the static pressure increases, as, for example, by the resistance of a passage into which the air is delivered, the volume of the delivery gradually decreases. If a curve is plotted between the delivery in cubic feet per minute represented .by horizontal coordinates and the static pressure by vertical coordinates, the curve starts on the base line for static pressure and out horizontally at a point corresponding to the maximum cubic feet per minute delivered by the blower. As the static pressure increases, the curve goes upward with a fairly steep backward slope for a considerable distance, but a point is soon reached where the curve slopes of! sharply at almost right angles.

' feet per minute delivered up to a certain point,

but. when the static pressure goes above a certain amount, the cubic feet per minute delivered drops off very rapidly. The blower ill in the present invention is of such capacity that it operates to deliver the proper volume of air at the proper static ressure while the blower is operating on the steep slope of the curve so that any increase in static pressure will not result in any marked decrease in the volume of supply.

Instead of using the usual air deflector in the end 01' the tube 23, a closure 3| is provided having a plurality of holes 32 in it (Figs.,3, 4 and 5). These holes are formed in the closure 3| so as to give the air a swirling motion as it enters the fire box. The blower l0 builds up a relatively high static pressure behind the closure, the openings 32 being of such size and number as to cause air to be delivered .to the flre box in the proper quantity for efficient combustion. This static pressure must be considerably greaterthan the pressure created by a starting surge, or by any pulsating surge that may occur within the furnace. In other words, the air must be supplied in suiiicient quantity and in the proper manner for efllcient combustion; it must be supplied with considerable velocity pressure, and it must be backed by an air supply having a relatively high static pressure. The' action under conditions that tend to cause "panting is then as follows:

Assume that the furnace-is started and that a condition of high pressure has been caused by the ignition of the atomized oil. This pressure, however, is not equal to the pressure behind the incoming air. While the pressure within the combustion chamber tends to retard the incoming air, the eflect is relatively small owing to the velocity at which the air is entering and the static pressure behind it. The result is that the supply of air to the combustion chamber remains substantially constant. Under these circumstances the increased pressure does not affect the efficiency of combustion and a condition of low pressure is not created. Instead, the flame continues to burn steadily and the pressure created by the initial ignition tends to dissipate itself on the column of air and gases between the chamber and the top of the chimney. The constant supply of air'and the pressure behind it prevents'therhythmic action from starting. To

put it another way, while .the starting pressure tends to create a condition of pulsating, the incoming-alr chokes the pulsations.

While it is preferable, for reasons that will be explained later, to have the closure 3| for the air pipe 23 at the end of said pipe, it is also possible to have a closure, or baiile, located farther back in the pipe, as indicated at 40 in Fig. 5. In this form, the static pressure is created behind the baflle 40 and the air then goes out through a small opening in said baflle into the front end of the pipe where it is distributed by the usual type of deflector 24.

The exact form of apparatus used to get a static pressure behind the air supply while at the same time controlling said supplyso that only the proper quantity of air is delivered may take different forms and the above are merely illustrations.

The apparatus of Figs. 1-4 has the advantage that the end of the air delivery pipe 23 is closed. When this pipe is open a column of air extends from the blower to the delivery end of said pipe.

Since air is elastic and may be compressed or rarefled, the air column in the delivery pipe tends to magnify any unstable conditions that may exist in the combustion chamber. For example, if pressure insaid chamber is increased, the tendency is for the air in the delivery pipe to be compressed. If the pressure in the chamber is decreased, the air in the delivery pipe tends to be rarefied. This condition is improved with a closure in the end of the pipe having small openings for air delivery. While the combustion chamber is still in communication with the delivery pipe, the communication is through very small openings through which air is coming at high velocity andbehind which there is a very considerable static pressure. The air column in the delivery pipe does not magnify any unfavorable conditions in the chamber but. on the contrary, tends to resist changes in pressure in said chamber because the stabilizing effect of the high static pressure is eifective at the entrance to said chamber.

While several forms of apparatus have been shown, it is to be understood that the method of accomplishing the results does not depend upon the exact form of apparatus that may be used to put the method into effect. This method involves supplying fuel to an enclosed combustion chamber; supplying air to said chamber in proper quantities for efllcient combustion of said fuel; and of maintaining a static pressure behind said air supply higher than any pressure that may be created by a surge and thereby maintaining said air supply substantially constant in the face of changing conditions in said chamber.

I claim:

1. An anti-pulsating furnace'having an ensaid chamber, means for introducing combustion air into said chamber, said air-introducing means including a device for reducing the air supply near where it is introduced into said chamber, and means for supplying air to said air-introducing means behind said reducing device in such quantity and at such pressure that the static pressure of the air behind said reducing device is maintained considerably in excess of a y pressure that may occur in the comb tion chamber.

2. An anti-pulsating furnace having an enclosed combustion chamber that is substantially pressure tight except for the flue exit, means for introducing fuel under pressure into said chamber, an air-introducing tube .connecting with said chamber having a closure in its inner end provided with one or more small openings communicating with said chamber to introduce combustion air into said chamber and means for supplying air to said tube in such quantity and at such pressure as to maintain the air behind said closure at a high static air pressure'considerably in excess'of any pressure that may occur in said combustion chamber.

3. An anti-pulsating furnace having an enclosed combustion chamber which is substantially pressure tight except for the flue exit, a gun-type oil burner including oil and air delivery means for introducing oil and air into the combustion chamber, said air-delivery means including a device for reducing the air supply near where it is delivered into the chamber, and means for supplying air -to the air-delivery means behind oil burner including oil and air delivery means for introducing oil and air into the combustion chamber, said air delivery means comprising an m the static pressure of the air beair-introducing tube connecting with the chamber having a closure in its inner end provided with a plurality of small openings through which combustion air is introduced into the chamber, and means for supplying air to the tube in such quantity and at such pressure as to maintain the air behind the closure at a high static air pressure considerably in excess oi any pressure that may occur in the combustion chamber.

LOUIS E. ARNOLD. 

